The membrane localisation and diffusion of particular proteins within a cell is critical to the protein's and the the cell's functions. Lipid modifications are commonly employed by the cell to target proteins to the inner leaflet of the plasma membrane; the distribution and lateral mobility of such acylated proteins is the focus of our experiments. EGFP constructs were transfected into RBL cells and their diffusion as well as the partition between membrane and cytosolic labeling analyzed and characterized by FCS.